A hotly debated question in cognitive neuroscience is whether
individual instances of perceptual sequences, and the rules that
describe them, are processed by the same brain mechanisms.
We tested the hypothesis that such rules and instances are
processed by dissociable brain mechanisms. We analyzed
event-related brain potentials (ERPs) evoked during cognitive
sequencing tasks that assessed surface (instance) vs abstract
(rule) structure learning. Sequence instances ABCBAC and
DEFEDF have different serial order or surface structure, but
share the same rule or abstract structure, 123213. Nine
healthy subjects were ®rst trained to learn a set of surface and
abstract structures in sequences of visually presented stimuli.
During the subsequent ERP recording, for surface and abstract
structures, they then discriminated between acceptable and
unacceptable sequences, based on the pre-learned regularities.
Abstract structure processing evoked a late positivity around
500 ms, which was not seen in the surface structure proces-
sing, supporting our hypothesis of dissociable processes. We
discuss implications for the rule vs instance debate, and
similarities between this late positivity and the P600 observed
in previous studies of syntactic processing. NeuroReport
11:1129±1132 & 2000 Lippincott Williams & Wilkins.